feat(docs): add agent guide, build class patterns, log triage, and AI instructions

.github/skills/staticphp-build-troubleshooting/SKILL.md

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+---
+name: staticphp-build-troubleshooting
+description: Diagnose StaticPHP v3 failures. Use when investigating build, compile, linker, download, doctor, environment, CI, smoke-test, terminal output, spc.output.log, spc.shell.log, config.log, CMake logs, or user-provided error snippets from StaticPHP commands.
+---
+
+# StaticPHP Build Troubleshooting
+
+## Overview
+
+Use this skill to triage StaticPHP failures from the outside in: command and environment first, SPC module/stage metadata next, shell/config logs last. The goal is to isolate the failing package, stage, command, and root cause before editing code.
+
+## First Pass
+
+1. Capture the exact command, OS, architecture, PHP version, extensions/libs/targets, and whether the run used `-v`, `-vv`, or `-vvv`.
+2. Read the final terminal error first. StaticPHP prints module error info, failed package, failed stage, failed command, log paths, and extra log files when available.
+3. If log files exist, inspect them in this order:
+   - `log/spc.output.log`: user-facing SPC messages and exception summary.
+   - `log/spc.shell.log`: executed commands, working directories, env, stdout/stderr.
+   - Extra logs named in the exception output: `php-src.config.log`, `lib.<pkg>.console.log`, `lib.<pkg>.cmake-error.log`, `lib.<pkg>.cmake-configure.log`, `lib.<pkg>.cmake-output.log`.
+4. Read `references/log-triage.md` for pattern matching, likely causes, and next checks.
+
+## Diagnosis Rules
+
+- Do not start by changing shared core code. Most failures are package metadata, environment, upstream source, dependency order, or platform flags.
+- Prefer evidence from the last failing command over earlier warnings.
+- When logs are long, search backward for `Command exited`, `error:`, `undefined reference`, `not found`, `No package`, `CMake Error`, `configure: error`, `fatal error`, `Failed module`, and `Failed stage`.
+- Use `config.log` and CMake logs for configure detection failures; use `spc.shell.log` for the actual command and env.
+- Be careful with rebuild suggestions. `spc reset --with-download --yes` is destructive to caches; ask before clearing caches unless the user explicitly asked.
+
+## Repro Commands
+
+Use focused commands when reproducing:
+
+```bash
+php bin/spc doctor -vvv
+php bin/spc download --for-extensions="curl,openssl" --with-php=8.5 --parallel=4 --retry=3 -vvv
+php bin/spc build:libs "openssl" -vvv
+php bin/spc build:php "bcmath,openssl,curl" --build-cli -vvv
+php bin/spc dev:lint-config
+```
+
+Choose the smallest command that still reaches the failing package.
+
+## Fix Direction
+
+After finding the failing package/stage:
+
+- Package YAML issue: use `$staticphp-package-maintenance`, then edit `config/pkg/*` or `config/artifact/*`.
+- Build command or patch issue: inspect the package class under `src/Package/*`.
+- Environment issue: check `doctor`, toolchain classes, and `config/pkg/tool/*`.
+- Upstream download issue: check artifact type, regex, GitHub rate limiting, mirror behavior, and `GITHUB_TOKEN`.
+- Core exception/logging issue: inspect `src/StaticPHP/Exception`, `src/StaticPHP/Runtime/Shell`, or executor classes only after package-level causes are ruled out.
+
+## Resources
+
+- `references/log-triage.md`: log files, failure categories, search patterns, and likely fixes.